In this Career Development Award application, I will lay the foundation for epidemiological and genetic studies of circadian rhythm in human populations. This proposed study is designed to obtain valuable information for the planning of more comprehensive studies of circadian rhythm in the near future. Prior studies have suggested that the diurnal preference is heritable and changes in circadian clock are associated with aging. We hypothesize that diurnal preference, a component of circadian rhythm, is variable and heritable in the Old Order Amish (OOA) and it is associated with aging. The primary objectives of this research proposal are three-fold: (1) to investigate the association between human diurnal preference and aging-related phenotypes at a population level; (2) to characterize genetic epidemiology of diurnal preference, including a genome-wide linkage analysis; and 3) to evaluate the usefulness of actigraphy in the studies of circadian rhythm. We plan to collect information on diurnal preference using the Horne-Ostberg questionnaire from 1,000 participants in the Amish Family Cardiovascular Intervention Study (AFCVIS) and 300 Amish participants of the "Longevity Genes in Founder Populations Study" (LGFPS), two newly initiated studies designed for studying genetic determinants of cardiovascular diseases, osteoporosis, and longevity. In addition, we will obtain 7-day actigraph and sleep log records from 200 volunteers in the LGFP study. Extensive information on aging-related phenotypes and a 5-cM genome scan are already available in these people. Our goal is to efficiently expand our data collection to study diurnal preference, and eventually, circadian rhythm. This proposed family study in a genetically homogeneous founder population with an "old-fashioned" life style provides a unique opportunity to study diurnal preference in a large and free-living human population.